| As a bridge connecting users' communication to one another in cellular mobile communication system,the base station antenna can achieve transinformation between the mobile terminals through the mobile service switching center.It is very critical to mobile communication system.The base station antenna is increasingly becoming the bottleneck of restricting the performance of the system,which had been proved by the experience about the extensive-commerce of the fourth generation mobile communication and development test in full swing of the fifth generation mobile communication.For the key techniques of new generation wireless mobile communication,the problems and challenge about the miniaturized base station antenna are summarized as below: extending bandwidth to be compatible with multiple mobile communication standards;improving isolation to achieve full-duplex wireless communication;suppressing the surface wave transmission between the MIMO antenna array elements to reduce the correlation of wireless communication channels,thus achieving multipath interference reduction for the MIMO system and enhancing the communication capacity;improving the mutual coupling of radiation field between the transmitting and receiving antenna array of the wireless relay system to reduce system size and avoid self-excitation,eliminating no-signal areas to improve the mobile communication signal coverage.The breakthrough of the key technology of base station antenna for the new generation wireless mobile communication,not only has unlimited business value,but also is the frontier technology with great academic value in the antenna field,especially the studies on the antennas with high port isolation and decoupling technology.Based on the relevant fundamental theory of multiband/broadband antenna and artificial metamaterial,this dissertation focus on the following four aspects: the design of the multiband miniaturized antenna,the design of broadband antenna with high port isolation,the design of decoupling structure of MIMO antennas and the design of electromagnetic isolation structure for the wireless relay system.The main research contents and work of this dissertation are outlined as following:1.IntroductionFirstly,the research background and trends of the new generation wireless mobile communication are introduced.Then,the domestic and foreign research tendency on the key techniques of novel base station antenna for the new generation mobile wireless communications are reviewed,including the introduction on these three aspects: base station antenna for mobile wireless communication,artificial metamaterial and cancellation technology for the self-interference signal.Based on the research projects for my doctoral studies,main innovations of this dissertation are summarized.The main content and structural arrangement of this doctoral thesis are also introduced.2.The design of low profile dual-band dual-polarized antenna array with integrated feeding networkFirstly,the theoretical analysis is performed for microstrip antenna and feeding network.Then,some general design methods about the rectangular microstrip patch antenna,circular microstrip patch antenna,power dividers and directional coupler are also introduced.For the miniaturized and low profile micro base station antenna array over the Band 1 of 4G FDD-LTE,a novel dual-band dual-polarized antenna is proposed.The antenna is composed of a parasitic circular patch and a driven circular patch with quasi-cross-shaped slot.These two patches are etched on the top and bottom substrate,respectively.Being fed though the metallic via,the antenna can achieve good impedance matching,high port isolation and stable radiation pattern over the operational frequency band.Based on this antenna element,a simple passive network is proposed for 2×2 antenna array.The amplitude and phase of input signals of the array can be easily adjusted.The passive network is composed of four T-shape power dividers and two 3 dB quadrature couplers.By controlling the phase difference between the feeding ports,the beam width of the antenna array could be adjusted to realize beam forming.The simulation and measurement validate the feasibility of the design.3.The design of wideband dual-polarized magnetically coupled patch antenna array with extremely high port isolationFor the broadband micro base station antenna array with low profile and extremely high port isolation over the WIFI Band,Band 7 of 4G FDD-LTE and Band 38 of 4G TDD-LTE,a novel dual-polarized magnetically coupled microstrip patch antenna is proposed.The antenna is composed of a simple square patch and the feeding structures printed on the both sides of two vertical substrates.The feeding structures comprise a metal split loop,a metal split quasi-loop and a pair of open-ended transmission line.The square patch is fed by the novel feeding structures in the way of magnetically coupling.The antenna shows extremely high port isolation(better than 45 dB)over 20% impendence bandwidth(VSWR <1.5).The simulation and measured results make a good agreement.The error of the measured port isolation is also theoretically analyzed.4.The design of novel artificial periodic structure and passive self-interference cancellation networkFor the MIMO antenna array with extremely high port isolation over the Band 7 of 4G FDD-LTE and miniaturized broadband micro base station antenna with ultra-high port isolation over the Band 38 of 4G TDD-LTE,based on the above-mentioned magnetically coupled patch antenna,a novel artificial periodic structures(APS)and a passive cancellation network are proposed,respectively.The proposed APS and network could further improve the port isolation of the magnetically coupled patch antenna and the MIMO antenna array,respectively.The novel APS and passive cancellation network are fabricated and tested.Measured results showed that the two designs are able to achieve good isolation enhancement.5.The design of metamaterial cavity for the decoupling of wireless relay antenna arrayFirstly,the principle and simulation method about the metamaterial are introduced and summarized.For the miniaturized and low profile wireless relay antenna array over the Band 7 of 4G FDD-LTE and Band 38 of 4G TDD-LTE,based on the above-mentioned quasi-cross-shaped slotted antenna,a novel metamaterial back-cavity is proposed.The metamaterial cavity is composed of a pair of frequency selective surface(FSS),a pair of negative index material(NIM)and the metal reflector.They could form a metamaterial cavity for the antenna.Thus,this metamaterial cavity is able to achieve decoupling of each port for the two antennas.Due to the good decoupling effect of this cavity,it is redesigned and applied to the 2×4 backhaul antenna array of the wireless relay base station.The simulation and measurement results show that the metamaterial cavity can achieve decoupling of the co-polarization ports,as well as the cross-polarization ports. |
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